In the stage and studio industry, various colored gels may be used in front of spot and flood lights to illuminate a stage with different colors. Exemplary stage lighting apparatus are disclosed in U.S. Pat. Nos. 5,446,637 and 4,890,208. The gels used in such apparatus are typically made of plastic wrap-type or polyester sheets that have dyes in them to make them transmit different colors. Especially with respect to use in spot lights, colored gels that are saturated colors with a bluish or greenish hue have a limited life span before they bleach or burn and need to be replaced. Greenish gels especially are known to have a short life span compared to other colors.
Replacing each gel after it has become bleached or burned requires relatively expensive labor, since most stage lights are typically placed in precarious areas of the theater and there are usually many of them. The replacement of a gel by a stage hand between scenes may, for example, require a ladder and scaffolding. Even though a new gel may cost only a few pennies to purchase, the cost of replacing them during a show may cost several dollars. Furthermore, the more light out of a spot light or other such lighting fixtures, the shorter the life span of the gel. Nevertheless, manufacturers of spot lights are always looking for ways to get more light and high energy density out of their devices. It would be desirable, therefore, to be able to significantly extend the useful life of a colored gel and to enhance its performance without significantly reducing the amount of light available for use. The present invention fulfills that need by means of inserting a substrate having a thin film coating with certain reflectance properties between the colored gel and the light source of the lighting apparatus in which the gel is used.
Thin film technology has been used for a number of years to control the transmittance and/or reflectance of coated surfaces. By controlling the thickness and index of refraction of each film in a stack or array of thin films constituting a coating, one can tailor the reflective and transmissive characteristics of the coating. The design of such films and the principles used to achieve such results are well known to those skilled in the art as is the general knowledge of how to deposit the various thin films on various substrates. See, for example, MacLeod, H. A., Thin-Film Optical Filters (McGraw-Hill Publishing Co., N.Y. 1989); Thelen, Alfred, Design of Optical Interference Coatings (McGraw-Hill Book Co., N.Y. 1989); and Heavens, O. S., Optical Properties of Thin Solid Films (Dover, N.Y. 1965)
Various classes of coatings exist based not only upon the materials used to form said coatings, but based upon spectral reflectance characteristics as well. For instance, reflective coatings have long been available which transmit in the infrared region and reflect all or most of the visible portion of the spectrum. Such coatings are known generically as "cold mirrors." Alternately, coatings are also known which transmit the infrared portion of the spectrum and reflect only a fraction of the visible spectrum. These coatings are generically known as "color correcting cold mirror" coatings. Still other coatings, which reflect the infrared and transmit visible light, are known as "hot mirrors." They are used, for example, in overhead projectors. Coatings such as Optivex.RTM. are commercially available for use in filters to reflect UV but transmit visible light. They are sometimes used for track lighting and in museums to prevent fading of the dyes or pigments used in paintings or other exhibits.
For many commercial applications such coatings are provided on glass substrates in the form of reflector blanks or filter blanks. See, for instance, U.S. Pat. No. 4,380,794. Such coatings have many applications. For example, U.S. Pat. No. 5,169,229, discloses an optical coating deposited upon a plastic support article in order to shield the substrate from harmful UV (ultraviolet) radiation.
None of the cited references teach or suggest that a thin-film coating could effectively and efficiently extend the life of colored gels used in an optical assembly or a light fixture adapted to image a high-intensity beam of colored light at a distant location.